It is well known that down has exceptional insulating value per unit of weight. However, for the insulating value of the down to be obtained, it must be carefully loaded into sleeping bags, quilts, jackets or other articles employed to maintain a person warm. The high loft of down is largely responsible for its insulating value. However, if too much down is loaded into an article or if too little down is loaded into an article, the maximum benefit of the insulating value of the down is not obtained.
Down-filled articles are usually made as a series of tubes so that the migration of down is limited when the article is in use. The tubes are arranged in overlapped arrays or in other arrays so that the seams between adjacent tubes will be covered, on one side or the other, with a volume of down. The widely known fluffy and light character of down makes it very difficult to load properly. Ordinarily filling articles with down is accomplished in a "down room" because the light and fluffy character of the down makes its escape inevitable, messy and wasteful; and down rooms are employed because they tend to restrict the loss of down to a limited area. However, the fact that loading down is a messy job is the least of the problems because the escape of down is simply characteristic of the difficulties involved with measuring it, and after measurement loading it into an article. Down is usually measured by weight, and it is important not only that a down-filled article contain the proper weight of down but additionally that each of the tubes from which the article is made contain theh proper weight of down. It is evident that weighing a quantity of down is difficult because such small amounts occupy so much volume. It is also evident that once a weighed quantity of down is obtained, loading that weighed quantity into a fabric tube without loss is also difficult.
Down loading is conventionally accomplished by entraining a measured quantity of down in air, then passing the air with the down entrained through a nozzle that is inserted in a tube to be filled with down. The tubes are generally made of tightly woven fabric which makes them ideal for filtering the down from the air, resulting in a down-filled tube. Although down losses in the filling of the tube are greatly minimized by employing this technique, there is still a great deal of difficulty in measuring down and introducing it into an entraining air stream so that it may be delivered to a loading nozzle.